TiO2@Silica nanoparticles in a random laser: Strong relationship of silica shell thickness on scattering medium properties and random laser performance

Abstract

A TiO2@Silica nanoparticle has been introduced in a random laser. TiO2 particles with an average diameter of 0.41 μm were coated with silica shells of different thicknesses. Strong dependency of silica shell thickness on the medium scattering strength was found. A mathematical relationship between the scattering mean free path, random laser threshold, and random laser efficiency was developed. Higher efficiency, lower laser threshold, narrower bandwidth, and longest photobleaching lifetime were obtained in the random laser that had increased silica shell thickness. Optical colloidal stability and light coupling enhancement with scattering particles, provided by silica shell, should lead to improved laser performance.

Polydispersed Powders (Nd3+:YVO4) for Ultra Efficient Random Lasers

“…We attribute this effect to the following causes: (i) the presence of agglomerates of smaller particles (smaller than wavelength), such that the space between scattering surfaces is smaller than one wavelength. This should favor the near‐field coupling, which decreases the effective scattering strength . (ii) The agglomerates made of smaller particles should behave approximately like a bigger particle with a lower effective scattering cross‐section (lower effective refractive index).…”

“…On the contrary, a random laser composed by a homogeneous scattering medium with short transport mean free path would be pumped only from the front side of the sample, reducing considerably the volume and intensity of pumping and, consequently, its efficiency. A promising method called fraction of absorbed pumping (FAP) was used to study the absorption and diffusion processes in the samples, which allowed us to determine that the absorbance increases appreciably with the introduction of smaller grains between the big particles.…”

Observation of photonic paramagnetic to spin-glass transition in a specially designed TiO_2 particle-based dye-colloidal random laser

“…In spite of the promising characteristics of dye-based RLs, the dye photodegradation, enhanced due to the presence of the scatterers is a drawback for the basic investigation and practical application of these systems [21,23]. The most used scatterer particles material is TiO 2 in the rutile phase due to its high refractive index (~ 2.6 at 632.8 nm) that implies a large index contrast with the dye solution.…”

“…Then, a photocatalytic process is started leading to fast dye degradation [24]. Attempts to minimize the photodegradation were made using scatterer particles based on materials with large energy bandgap [21][22][23]. Indeed, silica particles, which have energy bandgap of ~ 5.0 eV and refractive index of ~ 1.7 in the visible range, have been used and lower photodegradation was observed [21][22][23].…”

“…Attempts to minimize the photodegradation were made using scatterer particles based on materials with large energy bandgap [21][22][23]. Indeed, silica particles, which have energy bandgap of ~ 5.0 eV and refractive index of ~ 1.7 in the visible range, have been used and lower photodegradation was observed [21][22][23]. However, two other important points neglected by most of researchers are the particles precipitation and the chemical bonding between the particles and the cuvette walls that contribute to reduce the efficiency and lifetime of the RLs.…”